1. Field of the Invention
The present invention relates to a method of fabricating a color filter substrate for a liquid crystal display (LCD) device, and more particularly, to a method of fabricating a color filter substrate having patterned spacers.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device makes use of optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientational alignment that results from their long thin shape. The orientation of the liquid crystal molecules can be controlled by applying an electric field to the liquid crystal molecules. The orientation of the liquid crystal molecules changes in accordance with an intensity of the applied electric field. Incident light through a liquid crystal material is refracted due to an orientation of the liquid crystal molecules. Thus, an intensity of the incident light can be controlled and images can be displayed.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superior display of moving images. In an active matrix LCD (AM-LCD) device, thin film transistors (TFTs) and pixel electrodes connected to the TFTs are disposed in a matrix configuration.
The LCD device includes upper and lower substrates, and a liquid crystal layer interposed therebetween. The upper substrate and lower substrate are commonly referred to as a color filter substrate and an array substrate, respectively. A common electrode and color filter layers are formed on the upper substrate. TFTs and pixel electrodes are formed on the lower substrate. A seal pattern is provided at a periphery of one of the upper and lower substrates for bonding the upper and lower substrates to each other.
After forming the common electrode, the color filter layers, the TFTs and the pixel electrodes, the LCD device undergoes a liquid crystal cell process where a liquid crystal layer is formed between the upper and lower substrates. The liquid crystal cell process may be divided into a process of forming an alignment layer to align the liquid crystal molecules, a process of forming a cell gap, a process of attaching the color filter and array substrates together, a process of cutting the attached color filter and array substrates into cells, and a process of injecting the liquid crystal molecules. Accordingly, a liquid crystal display panel is fabricated using the liquid crystal cell process.
FIG. 1 is a perspective view of a related art liquid crystal display device. Referring to FIG. 1, a liquid crystal display device 1 includes first and second substrates 10 and 60 arranged facing each other. A liquid crystal layer 80 is interposed between the first and second substrates 10 and 60. A color filter layer 65 and a common electrode 70 are subsequently formed on an inner surface of the second substrate 60. An electric field is applied to the liquid crystal layer 80 through the common electrode 70. Although not shown, the color filter layer 65 includes red, green and blue filters for passing only light of a specific wavelength, and a black matrix. The black matrix is disposed in a boundary region of the color filters and shields light from a region in which alignment of the liquid crystal layer 80 is uncontrollable. An additional light source such as a backlight (not shown), for example, is mounted on the back of the first substrate 10.
A plurality of gate lines 15 and a plurality of data lines 20 are formed in a matrix array on an inner surface of the first substrate 10. A plurality of TFTs “Tr” are disposed at crossings of the gate lines 15 and data lines 20, and pixel electrodes 30 that are connected to the TFTs Tr are disposed at pixel regions P defined by crossings of the gate and data lines 15 and 20. A TFT “Tr” is a switching device.
Although not shown, the LCD device 1 requires internal spacers to maintain a cell gap defined by a thickness of the liquid crystal layer 80. However, since ball spacers are randomly distributed between the first and second substrates 10 and 60, the quality of an alignment layer may be lowered due to movement of the ball spacers. In addition, light leakage may occur within regions adjacent to the ball spacers due to an adsorption force between the liquid crystal molecules adjacent to the ball spacers. Moreover, a uniform cell gap may not be obtained in a large sized LCD device. Furthermore, since the ball spacers are elastic and do not remain at a fixed position, a severe ripple phenomenon may occur when the LCD device 1 is touched. Thus, superior display quality can not be obtained in the LCD device 1 when a uniform cell gap is maintained using ball spacers.
On the other hand, a uniform cell gap may be easily obtained using patterned spacers since they are formed in a non-pixel region, thereby preventing light leakage and improving contrast ratio. In addition, the patterned spacers may be applied to an LCD device to form a small cell gap since the patterned spacers can be controlled precisely. Furthermore, since the patterned spacers are fixed, they may be easily applied to large sized LCD devices and the ripple phenomenon may be prevented when the LCD device is touched. Since the patterned spacers may be formed directly on the overcoat layer in a case of omitting a common electrode from the color filter substrate such as in an IPS-mode LCD device, reliability of the patterned spacers is improved.
FIG. 2 is a schematic plan view showing an LCD device having patterned spacers according to the related art. FIG. 3 is a schematic cross section view along a line III-III of FIG. 2. Referring to FIG. 2, a plurality of gate lines 15 is formed on the first substrate 10 (shown in FIG. 1) along a first direction. The plurality of gate lines 15 includes gate electrodes 13. Data lines 20 a formed along a second direction crossing the gate lines 15 to define pixel regions P. Thin film transistors TFTs “Tr” are connected to the gate lines 15 and the data lines 20.
Referring to FIG. 3, a gate insulating layer 17 is formed on the gate electrodes 13. A semiconductor layer 19 is formed by subsequently depositing an active layer 19a and an ohmic contact layer 19b on the gate insulating layer 17 over the gate electrodes 13. Source and drain electrodes 23 and 25 are formed on the semiconductor layer 19 with a space between the source and drain electrodes 23 and 25, thereby forming a channel “ch” exposing the active layer 19a. The TFTs “Tr” include the gate electrodes 13, the semiconductor layer 19 and the source and drain electrodes 23 and 25.
Moreover, a passivation layer 27 is formed on the TFT “Tr”, and a pixel electrode 30 is formed on the passivation layer 27. The passivation layer 27 has a plurality of drain contact holes 24 that expose a surface region of the drain electrode 25, and the pixel electrodes 30 contact the surface region of the drain electrode 25 through the plurality of drain contact holes 24 with the pixel region P.
A color filter layer 65 and a black matrix 62 are formed on an inner surface of the second substrate 60. The black matrix 62 includes a plurality of open portions 63 corresponding to the pixel regions P. A common electrode 70 is formed on the color filter layer 65 and the black matrix 62. Specifically, the color filter layer 65 includes red, green and blue color filters 65a, 65b and 65c. Each pixel region P includes one of red, green and blue color filters. The black matrix 62 is located in a boundary region of the pixel region P. Although not shown, the red, green and blue color filters 65a, 65b and 65c, respectively, are located in the open portions 63.
In order to improve image quality, the red, green and blue color filters 65a, 65b and 65c may overlap with edges of adjacent portion of the black matrix 62 as shown in FIG. 3. Although not shown, first and second alignment layers are formed on the pixel electrodes 30 and the common electrode 7, respectively, such that the liquid crystal layer 80 is formed between the first and second alignment layers.
Meanwhile, patterned spacers 85 are formed between the first and second substrates 10 and 60 to maintain a cell gap defined by a thickness of the liquid crystal layer 80. The patterned spacers 85 are spaced apart from each other, preferably, with a same interval. For example, the patterned spacers 85 are located in a periphery region of the pixel regions P. The patterned spacer 85 may be located in regions corresponding to portions of the gate lines 15 as shown in FIG. 3.
The patterned spacers 85 may be formed on the first substrate 10 or on the second substrate 60. However, since the second substrate 60 having the color filter layer 65 has a better flatness and a simpler structure than the first substrate 10, which includes an array element layer (not shown), the patterned spacers 85 are generally formed on the second substrate 60 having the color filter layer 65 in order to stabilize its position.
FIGS. 4A to 4G are schematic cross section views illustrating a fabricating process of a color filter substrate for an LCD device having patterned spacers according to the related art. Referring to FIG. 4A, a black matrix 62 is formed by coating (or depositing) a light blocking material on the second substrate 60 including the plurality of pixel regions P shown in FIG. 2. The black matrix 62 is located in a boundary of the pixel regions P in order to prevent leakage and to shield the TFT “Tr” (shown in FIG. 2) from incident light.
The black matrix 62 is formed by a photolithography process which may include steps of exposing and developing and may use a photoresist and a mask having a transmissive portion and a shielding portion. When the black matrix 62 is made of a photosensitive material, no photo-resist is required in the photolithography process. However, when the black matrix 62 is made of a metal containing a chromium (Cr) as a basic material, a photo-resist is required in the photolithography process. The black matrix 62 includes first to third open portions 63a, 63b and 63c, which expose portions of the second substrate 60, respectively. Each of the first to third open portions 63a, 63b and 63c corresponds each of the pixel regions P.
Referring to FIG. 4B, a red resist layer 64 is formed by spin coating or bar coating a red resist material over an entire surface of the second substrate 60 including the black matrix 62. Next, a mask 90 having a transmissive portion tp1 and a shielding portion sp1 is disposed over the second substrate 60. Then, the red resist layer 64 of the second substrate 60 is exposed by an ultraviolet (UV) light through the mask 90. For example, the red resist layer 64 may be a negative type material so that an exposed portion of the resist layer 64 is patterned into a desired pattern. Thus the transmissive portion tp1 of the mask 90 corresponds to the first open portion 63a in which a red color filter will be formed.
Referring to FIG. 4C, the exposed portion of the red resist layer 64 shown in FIG. 4B is patterned into a red color filter 65a. Although not shown, the red color filter 65a is completed by sequentially developing and curing after the step of exposing. The red color filter 65a is formed in the first open portion 63a of the black matrix 62. Furthermore, the red color filter 65a overlaps the edge of an adjacent black matrix 62 as shown in FIG. 4C.
Referring to FIG. 4D, green and blue sub color filters 65b and 65c are formed by patterning. The patterning includes sequentially coating, exposing and developing green and blue resist materials over the second substrate 60 having the red color filter 65a, respectively. The green and blue color filters 65b and 65c are located in the second and third open portions 63b and 63c, respectively. The red, green and blue color filters 65a, 65b and 65c constitute a color filter layer 65.
Referring to FIG. 4E, a common electrode 70 is formed on an entire surface of the color filter layer 65 and the black matrix 62 over the second substrate 60. For example, the common electrode 70 may be made of a transparent conductive material such as one of indium tin oxide (ITO), indium zinc oxide (IZO) and indium tin zinc oxide (ITZO).
Although not shown, when both of the common electrodes 70 and the pixel electrodes 30 shown in FIG. 3 are formed on the first substrate or array substrate 10, the common electrodes 70 is omitted from the second substrate or the color filter substrate 60. Also not shown, an overcoat layer may be formed between the color filter layer 65 and the common electrode 70 to improve planarization properties of the second substrate 60. In general, when the black matrix 62 is made of an organic material, the overcoat layer is formed on the second substrate 60.
Referring to FIG. 4F, a spacer material layer 84 is formed by coating a photosensitive organic material on the common electrode 70 over the second substrate 60. The photosensitive organic material includes a colorless transparent material. A mask 93 including a shielding portion sp2 and a transmissive portion tp2 is disposed over the second substrate 60 having the spacer material layer 84. The transmissive portion tp2 of the mask 93 is located at a boundary region of the shielding portion sp2. The spacer material layer 84 of the second substrate 60 is exposed by UV light through the mask 93. For example, the spacer material layer 84 is a negative type material having the same exposing property as the color filter layer 65.
Referring to FIG. 4G, following the developing process, only the exposed portion of the spacer material layer 84 corresponding to the transmissive portion tp2 of the mask 93 remains as shown in FIG. 4F. The remaining portion of the spacer material layer 84 shown in FIG. 4F acts as a patterned spacer 85. The patterned spacer 85 is located in a portion corresponding to the black matrix 62 as shown in FIG. 4G.
The fabricating method of the color filter substrate for the LCD device according to the related art requires at least five mask processes or photolithography processes for forming the black matrix, the red, green and blue color filters, and the patterned spacer. In these mask processes, a mask used in the mask processes is very expensive. In addition, since the number of mask processes is proportional to the number of masks, a large number of mask processes increases a production cost of the color filter substrate.